I'm sorry I didn't have time to read all the posts and stuff, but it looks like more than just a worn spring or overgassed condition. The impact is way too much.

Normally wouldn't the lower rear of the bolt carrier hit the trunion before that hammer cocking extension ever hits anything????

It's almost like there was some obstruction in the receiver that was hit. Broken hammer that was later replaced? Very curious.

I think the Bolt Carrier will have to be replaced. OR at least reshaped.

There are only 3 things that effect the force of which the bolt carrier is thrown back. Ammo, return spring, and gas pressure. With the top cover flying off, it's going to be gas pressure. Either he loads super hot ammo, or the gun is overgassed. I've never seen a worn spring let a bolt carrier hammer the trunnion that bad without help.

__________________
There are 3 kinds of people in this world.
The wise, learn from the mistakes of others.
The smart, learn from their own mistakes.
The others, well......they just never learn.

"Is life so dear, or peace so sweet, as to be purchased at the price of chains and slavery? Forbid it, almighty God! I know not what course others may take; but as for me, Give Me Liberty, Or Give Me Death!"
Patrick Henry.